This invention relates generally to packet switching. More especially the invention relates to a routing method and networks for switching asynchronous packets and possibly synchronous packets.
Asynchronous time-division switching is the known switching technique most suitable to meet the various constraints applying to the future of the wide band integrated services digital networks (ISDN-WB), notably adaptability, flexibility and evolutionary constraints. This technique provides for self-adaptation of the network enabling transmission with any source rate, which is a decisive advantage in view of the great variety of sources with different natures and performances, which should be connectable to a wide band network. Nevertheless, asynchronous time-division switching requires increased performances from the switches notably very short switching times to compensate for the delays due to buffer queues and to dispose of the high rates. To achieve short switching times, the switches should be of the simplest possible design. In view of present-day circuit integration techniques it is possible, at a reasonable cost, to provide the different terminals connectable to the network with a high level of "intelligence". A solution to simplify the operations performed by the switches would consist in giving to these intelligent terminals responsibility for the choice of the routes to be followed by the packets through the network. The processing algorithms located in the switches are then reduced to their simplest expressions. The use of memories to support translation tables, as included in most known switches, is avoided and the control circuits in the switches can be obtained via a few high-speed logic integrated circuits.
Moreover, the user installations to which the terminals to the wide band network are to be connected also involve problems. Installations of different sizes must be envisaged, from the smallest subscriber installation to the local business network.
It is desirable that a subscriber installation be extendable, from a simple connecting plug for a single terminal to a genuine mini-switching network providing for internal communications between terminals. These mini-networks should remain at an accessible cost level and be simple to use. The homogeneity between the different installations is an important condition in guaranteeing a low cost, simple use and extensibility of the installations. The transmission media, connecting plugs, switching techniques employed should be the same in the different installations. The connecting plugs should be preferably standardized, i.e. be capable of connecting all types of terminals. The user can thus change the location of his terminals without having to modify the installation. Distributed bus and distributed switching ring or chain type structures have been proposed for these installations, notably to minimize the wiring required.
Likewise local business networks should offer guarantees of terminal extensibility and portability. Homogeneity is also an important condition for these installations. Moreover, it is desirable that a local business network should offer the possibility of locating any terminal connected to the network and thus the person to which it is generally specifically attributed.